System for controlling air conditioners with a pilot duty humidistat and rated horsepower thermostat



Dec. 12, 1961 T. K. KJELLMAN 3,012,411 SYSTEM FOR CONTROLLING AIR CONDITIONERS WITH A PILOT DUTY HUMIDISTAT AND RATED HORSEPOWER THERMOSTAT Filed Nov. 3, 1959 PI G. l. [I -IUMID1STAT FIG. 2.

' INVENTOR THOMAS K.KJLLMAN ATTORNEY United States Patent 3,012,411 SYSTEM FOR CONTROLLING AIR CONDITIONERS WITH A PILOT DUTY HUMIDISTAT AND RATED HORSEPOWER THERMOSTAT Thomas K. Kjclirnan, Timoninm, Md., assignor to The Bendix Corporation, a corporation of Delaware Filed Nov. 3, 1959, Ser. No. 850,581 5 Claims. (Cl. 62-173) A desirable feature for certain air-conditioning systems is means for dehumidifying the ambient air in an enclosure without materially lowering its temperature below the desired comfort level. Refrigeration systems for accomplishing this function have heretofore been proposed; they incorporate means governed by a combination thermostat-humidistat arrangement for cycling the cold and warm refrigerant in heat-exchange relation with evaporator sections effective to first cool the ambient air below its dew point to dehumidify and then reheat the air to bring it back up to the temperature set by the thermostat. An economical yet highly effective refrigeration system for performing this desirable function is one wherein the evaporator coils are divided into two sections and a reversing or reheat valve is controllable to direct a portion of the warm refrigerant through the coils of one section while the remaining portion is cooled and expanded in the usual manner and directed through the coils of the other section. At other times when the air is being maintained at the set temperature, cooling with resultant dehumidification occur through the normal refrigeration process. However, in either case, a compressor or its functional equivalent must be kept running to efl'ect circulation of the refrigerant. In systems where the thermostat and humidistat operate independently of one another, both must be capable of controlling a compressor motor or other device by means of appropriate relays or a heavy duty type ofcontact mechanism; also there are times when it is of advantage to convert an air-conditioning system, for example a system of the window type governed by a rated horsepower thermostat, into one capable of dehumidifying without further cooling; and it is an object of the present invention to provide a simple low-cost circuit in air-conditioning systems of the above noted type whereby an ordinary light duty pilot humidistat may be hooked up with a rated horsepower thermostat in a manner such as'to obtain the desired control.

Another object is to provide an effective yet simple and economical combination thermostat-humidistat control for air-conditioning apparatus utilizing a refrigerating system having means effective to cool the ambient air to a selected temperature with resultant dehumidification, or first cool the air to dehumidify and reheatto the selected temperature.

The foregoing and other objects and advantages will become apparent in view of the following description taken. in conjunction with the drawing, wherein:

FIG. 1 illustrates more or less diagrammatically an air-conditioning system in accordance with the invention; and

FIG. 2 is a sectional view of a reheat or reversing valve for warm refrigerant.

The invention is directed primarily to the manner in which the humidistat and thermostat are hooked up with one another and with the compressor and reversing or reheat valve of the refrigeration system. Once the concept of the invention becomes known, it will be obvious grammatically since their equivalents may be purchased in the open market and modified, where such becomes necessary, at will.

Referring to the drawing, an enclosure to be conditioned is generally indicated at 10, air being drawn therefrom by way of a duct 11 to and through an evaporator chamber 12, and thence returned by way of fan housing 13 and duct 14 back to the enclosure 10.

The refrigeration system includes a compressor 15, driven by a motor 16, having a starting switch 17. A high pressure refrigerant line conducts warm refrigerant from the discharge side of the compressor through conduit 18, condenser coil 19 and thence by way of line 20 to expansion valve 21, which is shown purely by way of example and could of course be substituted by capillary tubes or similar restrictive connections. The valve 21 discharges into an evaporator 22, having a branch 23 communicating with the inlet end of evaporator section or coil 24, and another branch 25 communicating by way of valve chamber 26 with the inlet end (inlet during normal refrigeration cycle) of evaporator section or coil 2.7. An auxiliary cycle control solenoid valve 28 has a valve member 28' projecting into the valve chamber 26, said valve member when in its normally-closed position being spring-urged against a seat 29 and when in its retracted position engaging aseat 29. The seat 29. is at the entrance end of a warm refrigerant return conduit 30, which along with the coil 27 function as the reheat section of the evaporator when the valve member 28' is in its retracted position. Branch 25 of the evaporator is normally in communication by way of the valve chamber 26 with the coil 27, but when the valve member 28' is retracted against seat 29', the branch 25 is closed ofi from the coil 27 and the latter is placed in flow communication with the conduit 30. This conduit then provides a flow path for the warm refrigerant to the return side of the compressor by way of conduit 31, the conduit 31 being common to the evaporator coil 24.

A main reversing or reheat cycle control valve is generally indicated at 32; it is provided with a solenoid valve member 32', slidable to either one of two positions. As shown in FIG. 2, the solenoid 33 of valve member 32' is deenergized and the valve member in its normallyvclosed position, at which time it closes off or bars flow of warm refrigerant through a reverse or reheat cycle conduit 34 and open a refrigerant-return conduit section 35 for coil 27. When the solenoid 33 of the valve is energized, the reverse action takes place, i.e. the conduit 34 is opened and 35 closed. During the normal refrigerant cycle (without reheat) the refrigerant circulated through coil 27 returns to the compressor by way of conduit 36, chamber of valve 32, and conduit 35, the line 34 being then-blocked by valve member 32'. During the reheat cycle, with valve member 32' retracted, clearing conduit 34 and closing otf conduit 35, a portion of the warm refrigerant is conducted to coil 27 by way of conduit 34, chamber of valve 32 and conduit 36, and

since valve member 28 is then retracted, conduit 30 will be open and the warm refrigerant will flow through coil 27 and return by way of conduits 30 and 31.

A room thermostat is generally indicated at 38; it is provided with a thermal element in the form of a sensing bulb 39, connected through a tube 39' with a switch member 40, adapted to engage contact 41 or 42. The switch member 49 is connected to one side of the supply line, while the contact 42 is connected to the one terminal of the starter switch 17, the other terminal of said switch being connected to the other side of the line. The thermostat 38 should have a horsepower rating such as will take care of the relatively heavy duty relay or switch mechanism for the compressor motor 16. In the position of the thermostat switch 40 as shown in FIG. 1, the compressor motor is not running. However, should the ambient air rise to a temperature above that set by the thermostat, the fluid in the bulb 39 will expand and throw the switch 49 against contact 42, closing the circuit to the starting switch 17.

'A humidistat is schematically illustrated at 43; it is shown as having a humidity-responsive element 44, which in practice is made of human hair but which can be of any type responsive to changes in the moisture content of the air. The one end of said element is fixed or anchored as at 45, while the opposite or movable end thereof is connected to a switch 46, adapted to engage live contact 47 or limit contact 48. When the switch is closed against contact 47, thecircuit is completed across the supply line to (1) the solenoid 33 of the cycle control valve32, (2) a heating coil 50 and (3) the solenoid valve 28. The heating coil may be considered as an artificial heating means since it renders the room thermostat responsive to a selected temperature independent of room temperature.

An override thermostat 52 is operatively associated with the humidistat 43; it is shown in the form of a bi-metal coil having an arm 52' at its free end which is connected to the humidistat switch 46. This thermostat 52 functions to prevent closure of the humidistat switch 46 irrespective of the degree of relative humidity as long as the temperature of the ambient air is above a value determined by the setting of thermostat 52. During these periods, the

room thermostat 38 senses the temperature ofthe ambien-t air, which is cooled back down to the selected value and at the same time dehumidified as a result of moisture being deposited on the evaporator coils 24 and 27. However, should the temperature drop below a value set by the override thermostat 52 and the relative humidity rise above that set by the humidistat 43, the switch 46 will close and the ambient air will first circulate in heatexchange relationwith and be cooled by coil 24 to effect dehumidification and then be reheated to a given or selected temperature by coil 27 Operation Normal cooling with resultant dehumidification.Let it be assumed that the temperature is to be maintained at, for example, 75 F. at a relative humidity not to exceed 60% and the thermostat 38 is set so that switch 40 will engage contact 42 when the temperature exceeds 75 F. It can also be assumed that the humidistat 43 is set to close switch 46 against contact 47 at a realtive humidity of 60% but the override thermostat will not permit this to happen unless the temperature is below 75 F. As long as the switch 46 is open, the solenoid 33 of the main cycle control valve 32 will be unenergized and the valve member 32 will close the conduit 34; also, the solenoid of the auxiliary cycle control valve 28 will remain unenergized and the valve member 28' ,will close oil the entrance to conduit 30. ,Under these circumstances,

should the temperature exceed 75 F., switch 40 will close against contact 42, starting the compressor motor 16,

awhereupon refrigerant will. be circulated from the high pressure side of the compressor through conduit 18, condenser 19, conduit 20, expansion valve 21 and into evaporator 22. Since the valve member 23 is blocking the entrance tothe conduit 30, the expanded refrigerant will ,fiow through both branches 23 and 25 of the evaporator into and through the evaporator coils 24 and 27, extracting heat from the air passing through evaporator chamber 12, and the warm refrigerant will be returned to the low pressure side of the compressor from coil24 by way of conduit 31 and from coil 27 by way of conduit 36, the chamber of valve 32 and conduit 35. During this period cooling with resultant dehumidification occur through the normal refrigeration cycle. 7

Dehumidification with no net co0ling.Should the temperature drop below 75 F. at a relative humidity above energized, causing valve member 32' to open conduit 34 and close conduit 35; at the same time the solenoid of the auxiliary cycle control valve 28 will be energized causing valve member 28 to open the inlet to conduit 30 and close off refrigerant coil 27 from the evaporator branch 25. Also, current flowing through the heating coil 50 will heat the latter and thus cause the fluid in the bulb 39 to expand, closing the thermostat switch 40 against the contact 42. This will start the compressor motor, whereupon refrigerant will start to flow from the high-pressure side of the compressor by way of conduit 18. However, since conduit 34 is now open, the warm refrigerant will divide and a portion thereof will pass through the conduit 34, chamber of the valve 32, conduit 36 and into coil 27, flowing through the latter and back by way of conduits 3i) and 31 to the return side of the compressor; and the remaining portion thereof will flow through the condenser 19, conduit 2!), expansion valve 21, evaporator 22 and branch 23, to coil 24 and through the latter and thence return by way of conduit 31. This results in dehumidification with no substantial change in temperature of the ambient air since the coil 24 reduces the temperature of the air to a point where a certain amount of its moisture content is given up, while the coil 27 reheats the air to the selected temperature.

What I claim is: p 1. In air-conditioning apparatus utilizing a refrigeration system having a compressor. and at least two evaporator sections providedwith means including cycle control valve means for cycling the refrigerant from the delivery to the return side of the compressor in one direction through both sections for maximum cooling of the ambient air without reheating or through one section in one direction and through the other section in the opposite direction for cooling, dehumidifying and reheating the ambient air, a thermostatic switch for controlling the compressor in response 'to changes in temperature of the air to be conditioned, artificial heating means arranged to efiect closure of said switch at a selected temperature independent of ambient temperature, and a second switch responsive to changes in humidity of the ambient air operatively. connected to said cycle control valve means and also to said heating means for initiating a dehumidifying and reheat cycle by eifecting closure of said first switch at temperatures which would otherwise allow said latter switch to remain open. I

V 2. In air-conditioning apparatus utilizing a refrigeration system having an electrically-powered compressor and at least two evaporator sections provided with means including cycle control valve means for cycling the refiigerant from the delivery to the return side of the compressor in one direction through both sections for maximum cooling of the ambient air without reheating or through one section in one direction and through the other section in the opposite direction for cooling, dehumidifying and reheating the ambient air, a thermostat and associated circuitry for controlling the compressor having a thermal switch responsive to changes in temperature of the ambient air to be conditioned, artificial heating means arranged to effect closure of the thermostat switch independent of ambient air temperatures, a normally-open electric circuit for controlling said cycle control valve means and said heating means, and a humidistat having a switch responsive to changes in the humidity and temperature of the air to be conditioned adapted to close said circuit under predeterminedv conditions of humidity and temperature and energize said heating means 60%, switch46. will close against contact 47, whereupon the solenoid 33 of the main cycle control valve 32'will be and valve means and at the same time effect closure of said thermostatic switch and cause the'compressor t initiate a dehumidifying and reheat cycle.

3. 'Inair-conditioning apparatus utilizing a refrigeration system having an electrically-powered compressor and at least two evaporator sections provided with means including cycle control valve means for cycling the retrigerant from the delivery to the return side of the conipressor in one direction through both sections for maximum cooling of the ambient air without reheating or through one section in one direction and through the other section in the opposite direction for dehumidifying and reheating the ambient air, a thermostat provided with a switch and associated circuitry for controlling the compressor and a thermal element responsive to changes in temperature of the ambient air to be conditioned operatively connected to said switch, artificial heating means arranged to heat said thermal element and cause it to close the thermostatic switch under conditions of ambient air temperature which would otherwise cause said switch to remain open, an electric circuit including said cycle control valve means and said heating means, a humidistat provided with a switch adapted to close said circuit under predetermined conditions of relative humidity of the ambient air and energize said heating means and effec closure of said thermostatic switch and at the same time set said control valve for a dehumidifying and reheat cycle, and means responsive to changes in temperature of the air to be conditioned for preventing closure of said humidistat switch at ambient air temperature above a selected value.

4. In air-conditioning apparatus utilizing a refrigeration system having an electrically-powered compressor and at least two evaporator sections provided with means including cycle control valve means for cycling the refrigerant from the delivery to the return side of the compressor in one direction through both sections for maximum cooling of the ambient air without reheating or through one ection in one direction and through the other section in the opposite direction for cooling, dehumidifying and reheating the ambient air, a main thermostat provided with a switch and associated circuitry for controlling the compressor and a thermal element responsive to changes in temperature of the ambient air to be conditioned operatively connected to said switch, an electric heating element arranged to heat said thermal element and effect closure of the thermostatic switch under conditions of ambient air temperature which would otherwise maintain the switch open, a normally open electric circuit for controlling said cycle control valve and heating element, a humidistat provided with a switch adapted to close said circuit under predetermined conditions of ambient air, humidity and temperature and energize said heating means and effect closure of the thermostat switch and at the same time set said cycle control valve for a reheat cycle, and another thermostat operatively connected to said humidistat switch for preventing closure of said latter switch at temperatures above a predetermined vaiue.

5. In air-conditioning apparatus utilizing a refrigeration system having a compressor and at least two evaporator sections, electric means for circulating refrigerant through said sections, and valve means which when set in a first position causes the cold expanded refrigerant to flow through both said sections to cool the ambient air with resultant dehumidification and when set in a second position causes the cold expanded refrigerant to flow through one section and warm refrigerant to flow through the other section to first cool the ambient air to efiect dehumidification and to then reheat the air, a thermostatic switch for controlling said circulating means, said switch being set to close and energize said circulating means when the ambient air temperature rises above a selected value at which time said valve means is in its first position, artificial heating means for effecting closure of said switch at a selected temperature independent of ambient air temperatures, switch means for controlling said valve means and said artificial heating means, and means responsive to changes in humidity and temperature of the ambient air for controlling said switch means.

References Cited in the file of this patent UNITED STATES PATENTS 2,195,781 Newton Apr. 2, 1940 2,679,142 McGrath May 25, 1954 2,725,724 Rosen Dec. 6, 1955 

